The present invention relates generally to a method for cooling a lamp, and more particularly, to a method for cooling a lamp backlighting module of a liquid crystal display. Liquid crystal displays are widely used as displays for computers, calculators, and security systems. In addition, liquid crystal displays have been particularly useful in avionic instrumentation display units.
In general, liquid crystal displays function by controlling the transmissibility of light through a liquid crystalline material. The transmissibility of light through the liquid crystalline material is controlled by manipulating the orientation of the liquid crystalline material. The orientation of the liquid crystalline material may be adjusted by applying a voltage across the liquid crystalline material. Consequently, the light which is transmitted through a layer of liquid crystalline material may be controlled by changing the voltage.
The liquid crystalline material is not self-illuminating. The liquid crystal display matrix is backlighted such that light may be transmitted through the liquid crystalline material. Backlighting is commonly provided by a lamp backlighting module which is adapted to transmit light through the liquid crystalline material. In addition, a diffuser may be located between the liquid crystal display matrix and the lamp in order to blend the light or to facilitate viewing the display from a variety of angles.
Power must be supplied to the lamp in order to produce light. As a by-product of producing light, the lamp also generates heat. The heat generated by the lamp may compromise the reliability and performance of the lamp backlighting module and the liquid crystal display. In particular, excessive heat diminishes a lamp's luminance for a given power input. Moreover, excessive heat reduces the reliability of the lamp and potentially presents a fire hazard.
There are several different embodiments of lamp backlighting modules. One embodiment of a lamp backlighting module includes a lamp suspended in a cavity behind a liquid crystal display matrix and enclosed within a chassis. This embodiment does little to dissipate the heat generated by the lamp. As a result, the lamp may be prone to become excessively hot.
Another embodiment of a lamp backlighting module includes a lamp bonded to a lamp housing. In this embodiment, a portion of the heat generated by the lamp may be dissipated through the lamp housing. In order to achieve maximum heat transfer through the lamp housing, the lamp may be bonded along its entire length to the lamp housing by a heat transfer medium such as a thermally conductive adhesive. In addition, the lamp housing may be comprised of a thermally conductive material such as aluminum or any other material having heat transfer characteristics similar to aluminum. The lamp housing may also have fins, flanges, or other protrusions which are adapted to dissipate the heat generated by the lamp. Nevertheless, the lamp may still be prone to become excessively hot in this embodiment since only a portion of the heat is dissipated through the lamp housing.
It is known to ventilate the chassis of a liquid crystal display in order to further dissipate the heat generated by the lamp. However, the air flow through the vents alone may not be sufficient to maintain the lamp at its optimal temperature. It is also known to use fans to cool lamps, but the fans are constantly on in some devices which can cause other problems discussed hereinafter. Consequently, a need exists for an improved method for cooling a lamp backlighting module of a liquid crystal display.
In light of the shortcomings of known cooling methods, there is a need to provide an improved method for cooling a lamp backlighting module. A need also exists to effectively dissipate the heat generated by a lamp backlighting module without compromising the viewing angle or backlighting of a liquid crystal display. It is a further need to use a fan to efficiently dissipate the heat generated by a lamp backlighting module. It is yet another need to utilize a microprocessor to turn on the fan only when necessary to dissipate heat generated by a lamp backlighting module. Finally, there is a need to control the temperature of a lamp backlighting module in order to achieve constant optimal luminance for a given power input.
The present invention satisfies one or more of these needs by providing an improved method for cooling a lamp. The present invention will be described primarily with regard to a method for cooling a lamp backlighting module of a liquid crystal display. However, it should be recognized that the method of the present invention may be used to cool practically any lamp. It should also be recognized that the method of the present invention may be used to cool practically any type of lamp backlighting module of any type of display. In fact, it is preferred that the method of the present invention be used in conjunction with a lamp backlighting module that includes a lamp which is bonded to a lamp housing.
In general, a preferred method of the present invention begins by providing a predetermined power input to a lamp. As power is provided to the lamp, the temperature of the lamp is monitored. When the temperature of the lamp rises to a first predetermined temperature, one or more fans are turned on which are adapted to dissipate the heat generated by the lamp. After the fan(s) cool the lamp to a second, lower predetermined temperature, the fan(s) are turned off.
By using a fan to dissipate heat generated by a lamp backlighting module, the present invention may maintain the temperature of the lamp within a desired range. As a result, the present invention preferably increases the reliability and performance of the liquid crystal display. In particular, a preferred embodiment of the present invention minimizes the power necessary to achieve optimal luminance, and it enables the lamp to constantly produce optimal luminance for a constant power input. It also increases the reliability of the lamp, and it reduces the risk of fire.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following descriptions of the drawings and preferred embodiments.